The underground watersealed petroleum storage caverns are popularly used in petroleum reserve worldwide. The quality of rock mass should be evaluated accurately so as to guarantee the stability of caverns and rational support design. Taking 3 typical sections of 4 north caverns of a underground watersealed petroleum storage cavern for examples, the geological conditions and the distribution of joint are detected by means of geological investigation, 3D photogrammetric monitoring system (ShapeMetriX 3D) and radar detection. And then the rock masses of the test sections are classified by means of Qsystem classification method. The support scheme is decided according to similar projects and related criteria; and the supporting effect is examined by means of FLAC3D simulation and site monitoring method. The construction results show that the support design is rational and the stability of the rock can be guaranteed.